title: Ventrolateral medullary functional connectivity and the respiratory and central chemoreceptor-evoked modulation of retrotrapezoid-parafacial neurons.
abstract: The medullary ventral respiratory column (VRC) of neurons is essential for respiratory motor pattern generation; however, the functional connections among these cells are not well understood. A rostral extension of the VRC, including the retrotrapezoid nucleus/parafacial region (RTN-pF), contains neurons responsive to local perturbations of CO(2)/pH. We addressed the hypothesis that both local RTN-pF interactions and functional connections from more caudal VRC compartments--extending from the Bötzinger and pre-Bötzinger complexes to the ventral respiratory group (Böt-VRG)--influence the respiratory modulation of RTN-pF neurons and their responses to central chemoreceptor and baroreflex activation. Spike trains from 294 RTN-pF and 490 Böt-VRG neurons were monitored with multielectrode arrays along with phrenic nerve activity in 14 decerebrate, vagotomized cats. Overall, 214 RTN-pF and 398 Böt-VRG neurons were respiratory modulated; 124 and 95, respectively, were cardiac modulated. Subsets of these neurons were tested with sequential, selective, transient stimulation of central chemoreceptors and arterial baroreceptors; each cell's response was evaluated and categorized according to the change in firing rate (if any) following the stimulus. Cross-correlation analysis was applied to 2,884 RTN-pF↔RTN-pF and 8,490 Böt-VRG↔RTN-pF neuron pairs. In total, 174 RTN-pF neurons (59.5%) had significant features in short-time scale correlations with other RTN-pF neurons. Of these, 49 neurons triggered cross-correlograms with offset peaks or troughs (n = 99) indicative of paucisynaptic excitation or inhibition of the target. Forty-nine Böt-VRG neurons (10.0%) were triggers in 74 Böt-VRG→RTN-pF correlograms with offset features, suggesting that Böt-VRG trigger neurons influence RTN-pF target neurons. The results support the hypothesis that local RTN-pF neuron interactions and inputs from Böt-VRG neurons jointly contribute to respiratory modulation of RTN-pF neuronal discharge patterns and promotion or limitation of their responses to central chemoreceptor and baroreceptor stimulation.
authors.affiliation: Department of Molecular Pharmacology and Physiology and Neuroscience Program, School of Biomedical Sciences, University of South Florida College of Medicine, Tampa, Florida 33612-4799, USA.
authors.forename: Mackenzie M
authors.initials: MM
authors.lastname: Ott
authors.forename: Sarah C
authors.initials: SC
authors.lastname: Nuding
authors.forename: Lauren S
authors.initials: LS
authors.lastname: Segers
authors.forename: Bruce G
authors.initials: BG
authors.lastname: Lindsey
authors.forename: Kendall F
authors.initials: KF
authors.lastname: Morris
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001931:Brain Mapping; D002344:Carotid Body / Q000166:cytology / Q000502:physiology; D002415:Cats; D002628:Chemoreceptor Cells / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D008526:Medulla Oblongata / Q000166:cytology*; D008954:Models, Biological; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology; D010791:Phrenic Nerve / Q000502:physiology; D011311:Pressoreceptors / Q000502:physiology; D012125:Respiratory Center / Q000166:cytology / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology*; D013223:Statistics as Topic